Method of transmitting synchronization signal and apparatus therefor

ABSTRACT

A method of transmitting a synchronization signal block, which is transmitted by a base station in a wireless communication system, is disclosed in the present invention. The method includes the steps of mapping a synchronization signal block including a PSS (primary synchronization signal), an SSS (secondary synchronization signal), and a PBCH (physical broadcasting channel) to a plurality of symbols, and transmitting the synchronization signal block mapped to a plurality of the symbols to a user equipment. In this case, in a symbol mapped the PSS, in a symbol mapped the SSS, and in a symbol mapped the PBCH, centers of subcarriers to which the PSS, the SSS, and the PBCH are mapped are the same and the number of subcarriers to which the PBCH is mapped is greater than the number of subcarriers to which the PSS and the SSS are mapped.

CROSS-REFERENCE TO RELATED APPLICATIONS

Pursuant to 35 U.S.C. § 119(a), this application claims the benefit ofearlier filing date and right of priority to U.S. Patent Application No.62/444,302, filed on Jan. 9, 2017 and U.S. Patent Application No.62/502,543, filed on May 5, 2017, the contents of which are herebyincorporated by reference herein in their entirety.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a method of transmitting asynchronization signal in a wireless communication system, and moreparticularly, to a method of transmitting a synchronization signal blockincluding a PSS (primary synchronization signal), an SSS (secondarysynchronization signal), and a PBCH (physical broadcasting channel) andan apparatus therefor.

Discussion of the Related Art

A brief description will be given of a 3rd Generation PartnershipProject Long Term Evolution (3GPP LTE) system as an example of awireless communication system to which the present invention can beapplied.

FIG. 1 illustrates a configuration of an Evolved Universal MobileTelecommunications System (E-UMTS) network as an exemplary wirelesscommunication system. The E-UMTS system is an evolution of the legacyUMTS system and the 3GPP is working on the basics of E-UMTSstandardization. E-UMTS is also called an LTE system. For details of thetechnical specifications of UMTS and E-UMTS, refer to Release 7 andRelease 8 of “3rd Generation Partnership Project; TechnicalSpecification Group Radio Access Network”, respectively.

Referring to FIG. 1, the E-UMTS system includes a User Equipment (UE),an evolved Node B (eNode B or eNB), and an Access Gateway (AG) which islocated at an end of an Evolved UMTS Terrestrial Radio Access Network(E-UTRAN) and connected to an external network. The eNB may transmitmultiple data streams simultaneously, for broadcast service, multicastservice, and/or unicast service.

A single eNB manages one or more cells. A cell is set to operate in oneof the bandwidths of 1.25, 2.5, 5, 10, 15 and 20 Mhz and providesDownlink (DL) or Uplink (UL) transmission service to a plurality of UEsin the bandwidth. Different cells may be configured so as to providedifferent bandwidths. An eNB controls data transmission and reception toand from a plurality of UEs. Regarding DL data, the eNB notifies aparticular UE of a time-frequency area in which the DL data is supposedto be transmitted, a coding scheme, a data size, Hybrid Automatic RepeatreQuest (HARQ) information, etc. by transmitting DL schedulinginformation to the UE. Regarding UL data, the eNB notifies a particularUE of a time-frequency area in which the UE can transmit data, a codingscheme, a data size, HARQ information, etc. by transmitting ULscheduling information to the UE. An interface for transmitting usertraffic or control traffic may be defined between eNBs. A Core Network(CN) may include an AG and a network node for user registration of UEs.The AG manages the mobility of UEs on a Tracking Area (TA) basis. A TAincludes a plurality of cells.

While the development stage of wireless communication technology hasreached LTE based on Wideband Code Division Multiple Access (WCDMA), thedemands and expectation of users and service providers are increasing.Considering that other radio access technologies are under development,a new technological evolution is required to achieve futurecompetitiveness. Specifically, cost reduction per bit, increased serviceavailability, flexible use of frequency bands, a simplified structure,an open interface, appropriate power consumption of UEs, etc. arerequired.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to an apparatus andmethod thereof that substantially obviate one or more problems due tolimitations and disadvantages of the related art.

An object of the present invention is to provide a method oftransmitting a synchronization signal in a wireless communication systemand an apparatus therefor.

Technical tasks obtainable from the present invention are non-limitedthe above mentioned technical tasks. And, other unmentioned technicaltasks can be clearly understood from the following description by thosehaving ordinary skill in the technical field to which the presentinvention pertains.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein,according to one embodiment, a method of transmitting a synchronizationsignal block, which is transmitted by a base station in a wirelesscommunication system, includes the steps of mapping a synchronizationsignal block including a PSS (primary synchronization signal), an SSS(secondary synchronization signal), and a PBCH (physical broadcastingchannel) to a plurality of symbols, and transmitting the synchronizationsignal block mapped to a plurality of the symbols to a user equipment.In this case, in a symbol mapped the PSS, in a symbol mapped the SSS,and in a symbol mapped the PBCH, centers of subcarriers to which thePSS, the SSS, and the PBCH are mapped are the same and the number ofsubcarriers to which the PBCH is mapped is greater than the number ofsubcarriers to which the PSS and the SSS are mapped.

In this case, the PBCH is mapped to a plurality of symbols and thesymbol to which the SSS is mapped can be located between symbols towhich the PBCH is dedicatedly mapped.

And, all of the symbols to which the PBCH is mapped include a pluralityof DMRSs and a plurality of the DMRSs can be arranged with an equalinterval in the symbols to which the PBCH is mapped.

And, subcarrier spacing for the SSS is identical to subcarrier spacingfor the PBCH and the SSS can be mapped to at least one symbol among aplurality of the symbols to which the PBCH is mapped.

wherein subcarriers to which the PBCH is mapped, in the at least onesymbol to which the PBCH and the SSS are mapped, are located at the topor the bottom of a frequency axis of subcarriers to which the SSS ismapped and the PSS, the SSS, and the PBCH can be mapped to a pluralityof contiguous symbols.

To further achieve these objects and other advantages and in accordancewith the purpose of the invention, as embodied and broadly describedherein, according to a different embodiment, a base station transmittinga synchronization signal block in a wireless communication systemincludes an RF unit configured to transceive a radio signal with a userequipment and a processor configured to map a synchronization signalblock containing a PSS (primary synchronization signal), an SSS(secondary synchronization signal), and a PBCH (physical broadcastingchannel) to a plurality of symbols in a manner of being connected withthe RF unit, the processor configured to transmit the synchronizationsignal block mapped to a plurality of the symbols to the user equipment.In this case, in a symbol mapped the PSS, in a symbol mapped the SSS,and in a symbol mapped the PBCH, centers of subcarriers to which thePSS, the SSS, and the PBCH are mapped are the same and the number ofsubcarriers to which the PBCH is mapped is greater than the number ofsubcarriers to which the PSS and the SSS are mapped.

In this case, PBCH is mapped to a plurality of symbols and the symbol towhich the SSS is mapped can be located between symbols to which the PBCHis dedicatedly mapped.

And, all of the symbols to which the PBCH is mapped include a pluralityof DMRSs and a plurality of the DMRSs can be arranged with an equalinterval in the symbols to which the PBCH is mapped.

subcarriers to which the PBCH is mapped, in the at least one symbol towhich the PBCH and the SSS are mapped, are located at the top or thebottom of a frequency axis of subcarriers to which the SSS is mapped.

According to the present invention, it is able to more efficientlyperform initial access by efficiently transmitting a synchronizationsignal in a subframe.

It will be appreciated by persons skilled in the art that the effectsthat can be achieved with the present disclosure are not limited to whathas been particularly described hereinabove and other advantages of thepresent disclosure will be more clearly understood from the followingdetailed description.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 illustrates a configuration of an Evolved Universal MobileTelecommunications System (E-UMTS) network as an example of a wirelesscommunication system.

FIG. 2 illustrates a control-plane protocol stack and a user-planeprotocol stack in a radio interface protocol architecture conforming toa 3rd Generation Partnership Project (3GPP) radio access networkstandard between a User Equipment (UE) and an Evolved UMTS TerrestrialRadio Access Network (E-UTRAN).

FIG. 3 illustrates physical channels and a general signal transmissionmethod using the physical channels in a 3GPP system.

FIG. 4 illustrates a structure of a radio frame in a Long Term Evolution(LTE) system.

FIG. 5 illustrates a radio frame structure for transmitting an SS(synchronization signal) in LTE system.

FIG. 6 illustrates a structure of a downlink radio frame in the LTEsystem.

FIG. 7 illustrates a structure of an uplink subframe in the LTE system.

FIG. 8 illustrates examples of a connection scheme between TXRUs andantenna elements.

FIG. 9 illustrates an example of a self-contained subframe structure.

FIGS. 10 and 11 illustrate examples of applying a different numerologyaccording to a channel and a signal.

FIGS. 12 to 15 are diagrams for explaining a method of designing asynchronization signal.

FIGS. 16 to 20 are diagrams for explaining embodiments for a method ofmultiplexing a synchronization signal.

FIGS. 21 to 24 are diagrams for explaining a method of mapping areference signal in a PBCH (physical broadcast channel).

FIGS. 25 to 26 are diagrams for explaining a method of transmitting abeam swept control channel.

FIG. 27 is a diagram for explaining a method of mapping a DMRS(demodulation reference signal) in a PBCH.

FIGS. 28 to 31 are diagrams for explaining a PBCH performance effectwhen a DMRS is used in a PBCH according to an embodiment of the presentinvention.

FIGS. 32 to 38 are diagrams for explaining embodiments of multiplexing aPSS/SSS/PBCH in a synchronization signal.

FIGS. 39 to 40 are diagrams for explaining a method of configuring asynchronization signal burst and a synchronization signal burst set.

FIGS. 41 to 42 are diagrams for a method of indexing a synchronizationsignal and a method of indicating the index.

FIGS. 43 to 49 are diagram for a result of measuring performanceaccording to embodiments of the present invention.

FIG. 50 is a block diagram of a communication apparatus according to anembodiment of the present disclosure.

DETAILED DESCRIPTION OF THE INVENTION

The configuration, operation, and other features of the presentdisclosure will readily be understood with embodiments of the presentdisclosure described with reference to the attached drawings.Embodiments of the present disclosure as set forth herein are examplesin which the technical features of the present disclosure are applied toa 3rd Generation Partnership Project (3GPP) system.

Although the embodiment of the present invention is described based onan LTE system and an LTE-A system in this specification, the LTE systemand the LTE-A system are only exemplary and may be applied to allsystems corresponding to the aforementioned definition.

The term ‘Base Station (BS)’ may be used to cover the meanings of termsincluding Remote Radio Head (RRH), evolved Node B (eNB or eNode B),Reception Point (RP), relay, etc.

FIG. 2 illustrates control-plane and user-plane protocol stacks in aradio interface protocol architecture conforming to a 3GPP wirelessaccess network standard between a User Equipment (UE) and an EvolvedUMTS Terrestrial Radio Access Network (E-UTRAN). The control plane is apath in which the UE and the E-UTRAN transmit control messages to managecalls, and the user plane is a path in which data generated from anapplication layer, for example, voice data or Internet packet data istransmitted.

A PHYsical (PHY) layer at Layer 1 (L1) provides information transferservice to its higher layer, a Medium Access Control (MAC) layer. ThePHY layer is connected to the MAC layer via transport channels. Thetransport channels deliver data between the MAC layer and the PHY layer.Data is transmitted on physical channels between the PHY layers of atransmitter and a receiver. The physical channels use time and frequencyas radio resources. Specifically, the physical channels are modulated inOrthogonal Frequency Division Multiple Access (OFDMA) for Downlink (DL)and in Single Carrier Frequency Division Multiple Access (SC-FDMA) forUplink (UL).

The MAC layer at Layer 2 (L2) provides service to its higher layer, aRadio Link Control (RLC) layer via logical channels. The RLC layer at L2supports reliable data transmission. RLC functionality may beimplemented in a function block of the MAC layer. A Packet DataConvergence Protocol (PDCP) layer at L2 performs header compression toreduce the amount of unnecessary control information and thusefficiently transmit Internet Protocol (IP) packets such as IP version 4(IPv4) or IP version 6 (IPv6) packets via an air interface having anarrow bandwidth.

A Radio Resource Control (RRC) layer at the lowest part of Layer 3 (orL3) is defined only on the control plane. The RRC layer controls logicalchannels, transport channels, and physical channels in relation toconfiguration, reconfiguration, and release of radio bearers. A radiobearer refers to a service provided at L2, for data transmission betweenthe UE and the E-UTRAN. For this purpose, the RRC layers of the UE andthe E-UTRAN exchange RRC messages with each other. If an RRC connectionis established between the UE and the E-UTRAN, the UE is in RRCConnected mode and otherwise, the UE is in RRC Idle mode. A Non-AccessStratum (NAS) layer above the RRC layer performs functions includingsession management and mobility management.

DL transport channels used to deliver data from the E-UTRAN to UEsinclude a Broadcast Channel (BCH) carrying system information, a PagingChannel (PCH) carrying a paging message, and a Shared Channel (SCH)carrying user traffic or a control message. DL multicast traffic orcontrol messages or DL broadcast traffic or control messages may betransmitted on a DL SCH or a separately defined DL Multicast Channel(MCH). UL transport channels used to deliver data from a UE to theE-UTRAN include a Random Access Channel (RACH) carrying an initialcontrol message and a UL SCH carrying user traffic or a control message.Logical channels that are defined above transport channels and mapped tothe transport channels include a Broadcast Control Channel (BCCH), aPaging Control Channel (PCCH), a Common Control Channel (CCCH), aMulticast Control Channel (MCCH), a Multicast Traffic Channel (MTCH),etc.

FIG. 3 illustrates physical channels and a general method fortransmitting signals on the physical channels in the 3GPP system.

Referring to FIG. 3, when a UE is powered on or enters a new cell, theUE performs initial cell search (S301). The initial cell search involvesacquisition of synchronization to an eNB. Specifically, the UEsynchronizes its timing to the eNB and acquires a cell Identifier (ID)and other information by receiving a Primary Synchronization Channel(P-SCH) and a Secondary Synchronization Channel (S-SCH) from the eNB.Then the UE may acquire information broadcast in the cell by receiving aPhysical Broadcast Channel (PBCH) from the eNB. During the initial cellsearch, the UE may monitor a DL channel state by receiving a DownLinkReference Signal (DL RS).

After the initial cell search, the UE may acquire detailed systeminformation by receiving a Physical Downlink Control Channel (PDCCH) andreceiving a Physical Downlink Shared Channel (PDSCH) based oninformation included in the PDCCH (S302).

If the UE initially accesses the eNB or has no radio resources forsignal transmission to the eNB, the UE may perform a random accessprocedure with the eNB (S303 to S306). In the random access procedure,the UE may transmit a predetermined sequence as a preamble on a PhysicalRandom Access Channel (PRACH) (S303 and S305) and may receive a responsemessage to the preamble on a PDCCH and a PDSCH associated with the PDCCH(S304 and S306). In the case of a contention-based RACH, the UE mayadditionally perform a contention resolution procedure.

After the above procedure, the UE may receive a PDCCH and/or a PDSCHfrom the eNB (S307) and transmit a Physical Uplink Shared Channel(PUSCH) and/or a Physical Uplink Control Channel (PUCCH) to the eNB(S308), which is a general DL and UL signal transmission procedure.Particularly, the UE receives Downlink Control Information (DCI) on aPDCCH. Herein, the DCI includes control information such as resourceallocation information for the UE. Different DCI formats are definedaccording to different usages of DCI.

Control information that the UE transmits to the eNB on the UL orreceives from the eNB on the DL includes a DL/UL ACKnowledgment/NegativeACKnowledgment (ACK/NACK) signal, a Channel Quality Indicator (CQI), aPrecoding Matrix Index (PMI), a Rank Indicator (RI), etc. In the 3GPPLTE system, the UE may transmit control information such as a CQI, aPMI, an RI, etc. on a PUSCH and/or a PUCCH.

FIG. 4 illustrates a structure of a radio frame used in the LTE system.

Referring to FIG. 4, a radio frame is 10 ms (327200×Ts) long and dividedinto 10 equal-sized subframes. Each subframe is lms long and furtherdivided into two slots. Each time slot is 0.5 ms (15360×Ts) long.Herein, Ts represents a sampling time and Ts=1/(15 kHz×2048)=3.2552×10-8(about 33 ns). A slot includes a plurality of Orthogonal FrequencyDivision Multiplexing (OFDM) symbols or SC-FDMA symbols in the timedomain by a plurality of Resource Blocks (RBs) in the frequency domain.In the LTE system, one RB includes 12 subcarriers by 7 (or 6) OFDMsymbols. A unit time during which data is transmitted is defined as aTransmission Time Interval (TTI). The TTI may be defined in units of oneor more subframes. The above-described radio frame structure is purelyexemplary and thus the number of subframes in a radio frame, the numberof slots in a subframe, or the number of OFDM symbols in a slot mayvary.

FIG. 5 illustrates a radio frame structure for transmitting an SS(synchronization signal) in LTE system. In particular, FIG. 5illustrates a radio frame structure for transmitting a synchronizationsignal and PBCH in FDD (frequency division duplex). FIG. 5 (a) showspositions at which the SS and the PBCH are transmitted in a radio frameconfigured by a normal CP (cyclic prefix) and FIG. 5 (b) shows positionsat which the SS and the PBCH are transmitted in a radio frame configuredby an extended CP.

An SS will be described in more detail with reference to FIG. 5. An SSis categorized into a PSS (primary synchronization signal) and an SSS(secondary synchronization signal). The PSS is used to acquiretime-domain synchronization such as OFDM symbol synchronization, slotsynchronization, etc. and/or frequency-domain synchronization. And, theSSS is used to acquire frame synchronization, a cell group ID, and/or aCP configuration of a cell (i.e. information indicating whether to anormal CP or an extended is used). Referring to FIG. 5, a PSS and an SSSare transmitted through two OFDM symbols in each radio frame.Particularly, the SS is transmitted in first slot in each of subframe 0and subframe 5 in consideration of a GSM (Global System for Mobilecommunication) frame length of 4.6 ms for facilitation of inter-radioaccess technology (inter-RAT) measurement. Especially, the PSS istransmitted in a last OFDM symbol in each of the first slot of subframe0 and the first slot of subframe 5. And, the SSS is transmitted in asecond to last OFDM symbol in each of the first slot of subframe 0 andthe first slot of subframe 5. Boundaries of a corresponding radio framemay be detected through the SSS. The PSS is transmitted in the last OFDMsymbol of the corresponding slot and the SSS is transmitted in the OFDMsymbol immediately before the OFDM symbol in which the PSS istransmitted. According to a transmission diversity scheme for the SS,only a single antenna port is used. However, the transmission diversityscheme for the SS standards is not separately defined in the currentstandard.

Referring to FIG. 5, by detecting the PSS, a UE may know that acorresponding subframe is one of subframe 0 and subframe 5 since the PSSis transmitted every 5 ms but the UE cannot know whether the subframe issubframe 0 or subframe 5. That is, frame synchronization cannot beobtained only from the PSS. The UE detects the boundaries of the radioframe in a manner of detecting an SSS which is transmitted twice in oneradio frame with different sequences.

Having demodulated a DL signal by performing a cell search procedureusing the PSS/SSS and determined time and frequency parameters necessaryto perform UL signal transmission at an accurate time, a UE cancommunicate with an eNB only after obtaining system informationnecessary for a system configuration of the UE from the eNB.

The system information is configured with a master information block(MIB) and system information blocks (SIB s). Each SIB includes a set offunctionally related parameters and is categorized into an MIB, SIB Type1 (SIB1), SIB Type 2 (SIB2), and SIB3 to SIB8 according to the includedparameters.

The MIB includes most frequently transmitted parameters which areessential for a UE to initially access a network served by an eNB. TheUE may receive the MIB through a broadcast channel (e.g. a PBCH). TheMIB includes a downlink system bandwidth (DL BW), a PHICH configuration,and a system frame number (SFN). Thus, the UE can explicitly knowinformation on the DL BW, SFN, and PHICH configuration by receiving thePBCH. On the other hand, the UE may implicitly know information on thenumber of transmission antenna ports of the eNB. The information on thenumber of the transmission antennas of the eNB is implicitly signaled bymasking (e.g. XOR operation) a sequence corresponding to the number ofthe transmission antennas to 16-bit CRC (cyclic redundancy check) usedin detecting an error of the PBCH.

The SIB1 includes not only information on time-domain scheduling forother SIBs but also parameters necessary to determine whether a specificcell is suitable in cell selection. The UE receives the SIB1 viabroadcast signaling or dedicated signaling.

A DL carrier frequency and a corresponding system bandwidth can beobtained by MIB carried by PBCH. A UL carrier frequency and acorresponding system bandwidth can be obtained through systeminformation corresponding to a DL signal. Having received the MIB, ifthere is no valid system information stored in a corresponding cell, aUE applies a value of a DL BW included in the MIB to a UL bandwidthuntil system information block type 2 (SystemInformationBlockType2,SIB2) is received. For example, if the UE obtains the SIB2, the UE isable to identify the entire UL system bandwidth capable of being usedfor UL transmission through UL-carrier frequency and UL-bandwidthinformation included in the SIB2.

In the frequency domain, PSS/SSS and PBCH are transmitted irrespectiveof an actual system bandwidth in total 6 RBs, i.e., 3 RBs in the leftside and 3 RBs in the right side with reference to a DC subcarrierwithin a corresponding OFDM symbol. In other words, the PSS/SSS and thePBCH are transmitted only in 72 subcarriers. Therefore, a UE isconfigured to detect or decode the SS and the PBCH irrespective of adownlink transmission bandwidth configured for the UE.

Having completed the initial cell search, the UE can perform a randomaccess procedure to complete the accessing the eNB. To this end, the UEtransmits a preamble via PRACH (physical random access channel) and canreceive a response message via PDCCH and PDSCH in response to thepreamble. In case of contention based random access, it may transmitadditional PRACH and perform a contention resolution procedure such asPDCCH and PDSCH corresponding to the PDCCH.

Having performed the abovementioned procedure, the UE can performPDCCH/PDSCH reception and PUSCH/PUCCH transmission as a general UL/DLsignal transmission procedure.

The random access procedure is also referred to as a random accesschannel (RACH) procedure. The random access procedure is used forvarious usages including initial access, UL synchronization adjustment,resource allocation, handover, and the like. The random access procedureis categorized into a contention-based procedure and a dedicated (i.e.,non-contention-based) procedure. In general, the contention-based randomaccess procedure is used for performing initial access. On the otherhand, the dedicated random access procedure is restrictively used forperforming handover, and the like. When the contention-based randomaccess procedure is performed, a UE randomly selects a RACH preamblesequence. Hence, a plurality of UEs can transmit the same RACH preamblesequence at the same time. As a result, a contention resolutionprocedure is required thereafter. On the contrary, when the dedicatedrandom access procedure is performed, the UE uses an RACH preamblesequence dedicatedly allocated to the UE by an eNB. Hence, the UE canperform the random access procedure without a collision with a differentUE.

The contention-based random access procedure includes 4 steps describedin the following. Messages transmitted via the 4 steps can berespectively referred to as message (Msg) 1 to 4 in the presentinvention.

-   -   Step 1: RACH preamble (via PRACH) (UE to eNB)    -   Step 2: Random access response (RAR) (via PDCCH and PDSCH (eNB        to)    -   Step 3: Layer 2/Layer 3 message (via PUSCH) (UE to eNB)    -   Step 4: Contention resolution message (eNB to UE)

On the other hand, the dedicated random access procedure includes 3steps described in the following. Messages transmitted via the 3 stepscan be respectively referred to as message (Msg) 0 to 2 in the presentinvention. It may also perform uplink transmission (i.e., step 3)corresponding to PAR as a part of the ransom access procedure. Thededicated random access procedure can be triggered using PDCCH(hereinafter, PDCCH order) which is used for an eNB to indicatetransmission of an RACH preamble.

-   -   Step 0: RACH preamble assignment via dedicated signaling (eNB to        UE)    -   Step 1: RACH preamble (via PRACH) (UE to eNB)    -   Step 2: Random access response (RAR) (via PDCCH and PDSCH) (eNB        to UE)

After the RACH preamble is transmitted, the UE attempts to receive arandom access response (RAR) in a preconfigured time window.Specifically, the UE attempts to detect PDCCH (hereinafter, RA-RNTIPDCCH) (e.g., a CRC masked with RA-RNTI in PDCCH) having RA-RNTI (randomaccess RNTI) in a time window. If the RA-RNTI PDCCH is detected, the UEchecks whether or not there is a RAR for the UE in PDSCH correspondingto the RA-RNTI PDCCH. The RAR includes timing advance (TA) informationindicating timing offset information for UL synchronization, UL resourceallocation information (UL grant information), a temporary UE identifier(e.g., temporary cell-RNTI, TC-RNTI), and the like. The UE can performUL transmission (e.g., message 3) according to the resource allocationinformation and the TA value included in the RAR. HARQ is applied to ULtransmission corresponding to the RAR. In particular, the UE can receivereception response information (e.g., PHICH) corresponding to themessage 3 after the message 3 is transmitted.

A random access preamble (i.e. RACH preamble) consists of a cyclicprefix of a length of TCP and a sequence part of a length of TSEQ. TheTCP and the TSEQ depend on a frame structure and a random accessconfiguration. A preamble format is controlled by higher layer. The RACHpreamble is transmitted in a UL subframe. Transmission of the randomaccess preamble is restricted to a specific time resource and afrequency resource. The resources are referred to as PRACH resources. Inorder to match an index 0 with a PRB and a subframe of a lower number ina radio frame, the PRACH resources are numbered in an ascending order ofPRBs in subframe numbers in the radio frame and frequency domain. Randomaccess resources are defined according to a PRACH configuration index(refer to 3GPP TS 36.211 standard document). The RACH configurationindex is provided by a higher layer signal (transmitted by an eNB).

In LTE/LTE-A system, subcarrier spacing for a random access preamble(i.e., RACH preamble) is regulated by 1.25 kHz and 7.5 kHz for preambleformats 0 to 3 and a preamble format 4, respectively (refer to 3GPP TS36.211).

FIG. 6 illustrates exemplary control channels included in a controlregion of a subframe in a DL radio frame.

Referring to FIG. 6, a subframe includes 14 OFDM symbols. The first oneto three OFDM symbols of a subframe are used for a control region andthe other 13 to 11 OFDM symbols are used for a data region according toa subframe configuration. In FIG. 5, reference characters R1 to R4denote RSs or pilot signals for antenna 0 to antenna 3. RSs areallocated in a predetermined pattern in a subframe irrespective of thecontrol region and the data region. A control channel is allocated tonon-RS resources in the control region and a traffic channel is alsoallocated to non-RS resources in the data region. Control channelsallocated to the control region include a Physical Control FormatIndicator Channel (PCFICH), a Physical Hybrid-ARQ Indicator Channel(PHICH), a Physical Downlink Control Channel (PDCCH), etc.

The PCFICH is a physical control format indicator channel carryinginformation about the number of OFDM symbols used for PDCCHs in eachsubframe. The PCFICH is located in the first OFDM symbol of a subframeand configured with priority over the PHICH and the PDCCH. The PCFICHincludes 4 Resource Element Groups (REGs), each REG being distributed tothe control region based on a cell Identity (ID). One REG includes 4Resource Elements (REs). An RE is a minimum physical resource defined byone subcarrier by one OFDM symbol. The PCFICH is set to 1 to 3 or 2 to 4according to a bandwidth. The PCFICH is modulated in Quadrature PhaseShift Keying (QPSK).

The PHICH is a physical Hybrid-Automatic Repeat and request (HARQ)indicator channel carrying an HARQ ACK/NACK for a UL transmission. Thatis, the PHICH is a channel that delivers DL ACK/NACK information for ULHARQ. The PHICH includes one REG and is scrambled cell-specifically. AnACK/NACK is indicated in one bit and modulated in Binary Phase ShiftKeying (BPSK). The modulated ACK/NACK is spread with a Spreading Factor(SF) of 2 or 4. A plurality of PHICHs mapped to the same resources forma PHICH group. The number of PHICHs multiplexed into a PHICH group isdetermined according to the number of spreading codes. A PHICH (group)is repeated three times to obtain a diversity gain in the frequencydomain and/or the time domain.

The PDCCH is a physical DL control channel allocated to the first n OFDMsymbols of a subframe. Herein, n is 1 or a larger integer indicated bythe PCFICH. The PDCCH occupies one or more CCEs. The PDCCH carriesresource allocation information about transport channels, PCH andDL-SCH, a UL scheduling grant, and HARQ information to each UE or UEgroup. The PCH and the DL-SCH are transmitted on a PDSCH. Therefore, aneNB and a UE transmit and receive data usually on the PDSCH, except forspecific control information or specific service data.

Information indicating one or more UEs to receive PDSCH data andinformation indicating how the UEs are supposed to receive and decodethe PDSCH data are delivered on a PDCCH. For example, on the assumptionthat the Cyclic Redundancy Check (CRC) of a specific PDCCH is masked byRadio Network Temporary Identity (RNTI) “A” and information about datatransmitted in radio resources (e.g. at a frequency position) “B” basedon transport format information (e.g. a transport block size, amodulation scheme, coding information, etc.) “C” is transmitted in aspecific subframe, a UE within a cell monitors, that is, blind-decodes aPDCCH using its RNTI information in a search space. If one or more UEshave RNTI “A”, these UEs receive the PDCCH and receive a PDSCH indicatedby “B” and “C” based on information of the received PDCCH.

FIG. 7 illustrates a structure of a UL subframe in the LTE system.

Referring to FIG. 7, a UL subframe may be divided into a control regionand a data region. A Physical Uplink Control Channel (PUCCH) includingUplink Control Information (UCI) is allocated to the control region anda Physical uplink Shared Channel (PUSCH) including user data isallocated to the data region. The middle of the subframe is allocated tothe PUSCH, while both sides of the data region in the frequency domainare allocated to the PUCCH. Control information transmitted on the PUCCHmay include an HARQ ACK/NACK, a CQI representing a downlink channelstate, an RI for Multiple Input Multiple Output (MIMO), a SchedulingRequest (SR) requesting UL resource allocation. A PUCCH for one UEoccupies one RB in each slot of a subframe. That is, the two RBsallocated to the PUCCH are frequency-hopped over the slot boundary ofthe subframe. Particularly, PUCCHs with m=0, m=1, and m=2 are allocatedto a subframe in FIG. 7.

Hereinafter, channel state information (CSI) reporting will be describedbelow. In the current LTE standard, there are two MIMO transmissionschemes, open-loop MIMO operating without channel information andclosed-loop MIMO operating with channel information. Particularly in theclosed-loop MIMO, each of an eNB and a UE may perform beamforming basedon CSI to obtain the multiplexing gain of MIMO antennas. To acquire CSIfrom the UE, the eNB may command the UE to feed back CSI on a downlinksignal by allocating a PUCCH (Physical Uplink Control CHannel) or aPUSCH (Physical Uplink Shared CHannel) to the UE.

The CSI is largely classified into three information types, RI (RankIndicator), PMI (Precoding Matrix), and CQI (Channel QualityIndication). First of all, the RI indicates rank information of achannel as described above, and means the number of streams that may bereceived by a UE through the same time-frequency resources. Also, sincethe RI is determined by long-term fading of a channel, the RI may be fedback to an eNB in a longer period than a PMI value and a CQI value.

Second, the PMI is a value obtained by reflecting spatialcharacteristics of a channel, and indicates a precoding matrix index ofan eNB, which is preferred by the UE based on a metric such as signal tointerference and noise ratio (SINR). Finally, the CQI is a valueindicating channel strength, and generally means a reception SINR thatmay be obtained by the eNB when the PMI is used.

In the 3GPP LTE-A system, the eNB may configure a plurality of CSIprocesses for the UE, and may be reported CSI for each of the CSIprocesses. In this case, the CSI process includes CSI-RS resource forspecifying signal quality and CSI-IM (interference measurement)resource, that is, IMR (interference measurement resource) forinterference measurement.

Since a wavelength becomes short in the field of Millimeter Wave (mmW),a plurality of antenna elements may be installed in the same area. Inmore detail, a wavelength is 1 cm in a band of 30 GHz, and a total of64(8×8) antenna elements of a 2D array may be installed in a panel of 4by 4 cm at an interval of 0.5 lambda (wavelength). Therefore, a recenttrend in the field of mmW attempts to increase coverage or throughput byenhancing BF (beamforming) gain using a plurality of antenna elements.

In this case, if a transceiver unit (TXRU) is provided to control atransmission power and phase per antenna element, independentbeamforming may be performed for each frequency resource. However, aproblem occurs in that effectiveness is deteriorated in view of costwhen TXRU is provided for all of 100 antenna elements. Therefore, ascheme is considered, in which a plurality of antenna elements aremapped into one TXRU and a beam direction is controlled by an analogphase shifter. Since this analog beamforming scheme may make only onebeam direction in a full band, a problem occurs in that frequencyselective beamforming is not available.

As an intermediate type of digital BF and analog BF, a hybrid BF havingB TXRUs smaller than Q antenna elements may be considered. In this case,although there is a difference depending on a connection scheme of BTXRUs and Q antenna elements, the number of beam directions that enablesimultaneous transmission is limited to B or less.

FIG. 8 illustrates examples of a connection scheme between TXRUs andantenna elements.

(a) of FIG. 8 illustrates that TXRU is connected to a sub-array. In thiscase, the antenna elements are connected to only one TXRU. Unlike (a) ofFIG. 8, (b) of FIG. 8 illustrates that TXRU is connected to all antennaelements. In this case, the antenna elements are connected to all TXRUs.In FIG. 8, W indicates a phase vector multiplied by an analog phaseshifter. That is, a direction of analog beamforming is determined by W.In this case, mapping between CSI-RS antenna ports and TXRUs may be1-to-1 or 1-to-many.

As more communication devices require greater communication capacity,the need of mobile broadband communication more advanced than theconventional RAT (radio access technology) has been issued. Also,massive MTC (Machine Type Communications) technology that providesvarious services anywhere and at any time by connecting a plurality ofdevices and things is one of main issues which will be considered innext generation communication. Furthermore, a communication systemdesign considering service/UE susceptible to reliability and latency hasbeen discussed. Considering this status, the introduction of the nextgeneration RAT has been discussed, and the next generation RAT will bereferred to as NewRAT in the present invention.

A self-contained subframe structure shown in FIG. 9 is considered in thefifth generation NewRAT to minimize data transmission latency in a TDDsystem. FIG. 9 illustrates an example of a self-contained subframestructure.

In FIG. 9, oblique line areas indicate downlink control regions andblack colored areas indicate uplink control regions. Areas having nomark may be used for downlink data transmission or uplink datatransmission. In this structure, downlink transmission and uplinktransmission are performed in due order within one subframe, wherebydownlink data may be transmitted and uplink ACK/NACK may be receivedwithin the subframe. As a result, the time required for datare-transmission may be reduced when an error occurs in datatransmission, whereby latency of final data transfer may be minimized.

In this self-contained subframe structure, a time gap for switching froma transmission mode to a reception mode or vice versa is required forthe eNB and the UE. To this end, some OFDM symbols (OS) at the time whena downlink is switched to an uplink in the self-contained subframestructure are set to a guard period.

Examples of the self-contained subframe type that may be configured inthe system operating based on the NewRAT may consider four subframetypes as follows.

-   -   downlink control period+downlink data period+GP+uplink control        period    -   downlink control period+downlink data period    -   downlink control period+GP+uplink data period+uplink control        period    -   downlink control period+GP+uplink data period

In the following, a method of configuring a synchronization signal isexplained according to embodiments of the present invention. Morespecifically, a method of configuring a synchronization signal block (SSblock), a synchronization signal burst (SS burst), and a synchronizationsignal burst set (SS burst set) is explained according to theembodiments of the present invention.

Unlike a legacy LTE system, as shown in the following, variousnumerologies are considered in a next generation mobile communication.

Subcarrier spacing: 15 kHz×2n (n=0,1,2,3, . . . ), 15 kHz×m (m=1,2,3, .. . )

Spectrum allocation: 20 MHz, 40 MHz, 80 MHz, 160 MHz . . . . In the nextgeneration mobile communication, a BRS (beam selection reference signal)corresponding to a reference signal for selecting a best beam from amonga plurality of beams is transmitted. In order to transmit the BRS, aplurality of OFDM symbols are required and an overhead problem mayoccur. As a result, complexity in designing a synchronization signal mayincrease in the next generation mobile communication system in whichvarious numerologies are allowed. In order to reduce the complexity indesigning the synchronization signal, the present invention proposesvarious methods in the following.

1. Numerology

Numerology including a CP length and subcarrier spacing can bedifferently applied to a channel and a signal defined in a physicallayer of a mobile communication system. In particular, when there arechannels and signals newly defined for a specific purpose as well aschannels and signals such as a shared channel (SCH), a control channel(CCH), a broadcasting channel (BCH), a synchronization signal (SS), achannel state information reference signal (CSI-RS), a soundingreference signal (SRS), a data demodulation reference signal (DMRS), arandom access channel (RACH), a multicast channel (MCH), and the like,as shown in the following embodiments, each of the channels and thesignals can be designed to have a different numerology.

1. Embodiment 1

In a beam-formed system providing coverage using a plurality of beams, amethod of transmitting a signal when an appropriate beam direction isobtained between a transmission point and a reception point may differfrom a method of transmitting a signal when it fails to obtain a beamdirection. For example, when a control channel and a data channel aretransmitted, it is preferable to perform signal transmission after abeam appropriate for enhancing signal quality between a transmissionpoint and a reception point is selected. On the other hand, in case ofInitial access, Paging, Random access, Scheduling Request, and the liketo be delivered by a TRP (transmission reception point) and a UE locatedat a random position before a beam appropriate for both directions isselected, it may be preferable to forward information in each directionto which a plurality of beams are heading. In this case, each ofchannels and signals can be designed with a different numerology.

For example, as shown in FIG. 10 (a), channels and signals can bedesigned to have the same symbol duration irrespective of a type of thechannels and a type of the signals. Or, as shown in FIG. 10 (b), a PSS,an SSS, a PBCH, a BRS and a paging signal can be transmitted via a shortOFDM symbol. An SCH, a CCH, and a DMRS can be transmitted via a longOFDM symbol.

On the other hand, in some cases, as shown in FIG. 10 (c), a PSS, anSSS, a PBCH, a BRS and a paging signal can be transmitted via a longOFDM symbol, whereas an SCH, a CCH, and a DMRS can be transmitted via ashort OFDM symbol.

2. Embodiment 2

A numerology set including subcarrier spacing, a CP length, and the likeof a shared channel (SCH) for transmitting data and a control channel(CCH) for transmitting control information can be configured in a mannerof being different from a numerology set including a synchronizationsignal (SS) for performing initial access, a broadcasting channel (BCH)on which essential system information is transmitted, a paging controlchannel (PCCH) in charge of paging, a beam selection reference signal(BSR) for selecting a beam, and the like.

Specifically, when there are various subcarrier spacing (e.g., 15, 30,60, 75, 120, 150, 240, . . . KHz) supported by a system, it may be ableto configure a channel and a signal for forwarding data and controlinformation to use all subcarrier spacing as much as possible.

On the contrary, a channel and a signal for performing initial access,paging, broadcasting, and the like are configured with subcarrierspacing (e.g., 15, 60, 240 kHz) of a limited value.

For example, in case of using numerology configured with subcarrierspacing of 15 kHz and a CP length of 4.69 us to transmit data, PSS/SSScan be configured with numerology identical to numerology of SCH or thePSS/SSS can be configured with subcarrier spacing (e.g., 60 kHz) widerthan that of the SCH.

As a different example, when PSS/SSS is transmitted with specificnumerology (e.g., subcarrier spacing of 15 kHz), different channelstransmitted on a component carrier including the PSS/SSS can beconfigured by various numerologies (e.g., 15, 30, 60 kHz, etc.).

As a further different example, when PSS/SSS is transmitted withspecific numerology (e.g., subcarrier spacing of 60 kHz), differentchannels transmitted on a component carrier including the PSS/SSS can beconfigured by various numerologies (e.g., 60, 120 kHz, etc.). As afurther different example, when PSS/SSS is transmitted on 15 kHz, a BRScan be transmitted on 60 kHz.

3. Embodiment 3

A CP length applied to a channel and a signal for forwarding data andcontrol information can be independently configured irrespective of a CPlength applied to a channel and a signal for performing initial access,paging, and broadcasting.

When a PSS/SSS is configured with wider subcarrier spacing, if CPoverhead is maintained with a legacy level (e.g., 4.69 us/66.667 us=7%),a CP length become shorter as much as 1/N (e.g., N=4, 15 kHz×N=60 kHz,4.69 us×1/N=1.172 us). In this case, if delay spread becomes longersimilar to a case that a cell radius is long or multi-TRP transmissionis performed, it may cause inter-symbol interference.

In order to solve the inter-symbol interference problem, when a PSS/SSS,a paging signal, a broadcasting channel, or a beam selection signal isconfigured using symbol duration shorter than SCH, it may consider amethod of matching a CP length with a length of the SCH.

For example, when PSS/SSS transmission time of a legacy LTE systemcorresponds to (4.69 us+66.667 us)×2=142.714 us, in order to transmitPSS/SSS of wider subcarrier spacing during the time, it may use 8 OFDMsymbols having a length of 17.839 us (=1.1725 us+16.667 us). In thiscase, since a CP length becomes shorter (4.69 us→1.1725 us), it may bedifficult to handle delay spread of legacy coverage.

Hence, if a method of extending a CP length and reducing the number ofsymbols is applied, it may consider designing a CP length of 3.8 us and7 OFDM symbols. (142.8 us=7×20.4 us=7×(3.8 us+16.667 us).

As shown in FIGS. 11 (a) and (b), if a length of an OFDM symbol isdifferentiated according to subcarrier spacing, it is able to see that aCP length becomes shorter in proportion to the length of the OFDMsymbol. As shown in FIG. 11 (c), it may be able to generate an OFDMsymbol robust to ISI by increasing CP overhead. For example, SCH istransmitted using a method shown in FIG. 11 (a) and SS/BCH/BRS can betransmitted using a method shown in FIG. 11 (a) or FIG. 11 (c).

4. Embodiment 4

It may configure time duration for which a common signal/channel istransmitted and beam sweeping can be performed as many as the number ofOFDM symbols included in the time duration. Or, it may be able to definesingle beam transmission or multi-beam transmission according to alength of OFDM symbols included in the time duration.

Time duration shown in FIG. 11 is defined as duration for which a commonsignal/channel is transmitted. As shown in FIG. 11 (a), if two OFDMsymbols are transmitted during the time duration, assume that a beamchange occurs in each OFDM symbol and two beams are used. As shown inFIG. 11 (b), if eight OFDM symbols are transmitted during the timeduration, assume that a different beam is transmitted in each of theeight OFDM symbols.

Or, the time duration shown in FIG. 11 is defined as duration for whicha common signal/channel is transmitted. As shown in FIG. 11 (a), if along OFDM symbol is transmitted, assume that single beam transmission isperformed. As shown in FIG. 11 (b), if a short OFDM symbol istransmitted, assume that multi-beam transmission is performed.

2. Common Design

When a signal for performing initial access is configured in a systemincluding various numerologies, the present invention proposes methodsof designing the signal to be common to each of the numerologies as muchas possible.

1. Embodiment 1

When a synchronization signal is designed, if a sequence is mapped usingN number of subcarriers, it may use the N number of subcarriersirrespective of a length of subcarrier spacing.

In particular, as shown in FIG. 12, when N numbers of sequences are usedand a synchronization signal is configured by mapping the sequences to M(>N) number of subcarriers, the M number of subcarriers are commonlyused by a symbol having narrow subcarrier spacing and a symbol havingwide subcarrier spacing.

For example, when 72 subcarriers are used, if subcarrier spacingcorresponds to 15 kHz, it may use a bandwidth of 1.08 MHz (=72×15 kHz).If subcarrier spacing corresponds to 60 kHz, it may use a bandwidth of4.32 MHz (=72×60 kHz).

2. Embodiment 2

Duration of an OFDM symbol having narrow subcarrier spacing becomeslonger, whereas duration of an OFDM symbol having wide subcarrierspacing becomes shorter. In this case, total time duration used forsynchronization is used with a similar level irrespective of subcarrierspacing.

For example, as shown in FIG. 13 (a), if two OFDM symbols are used whensubcarrier spacing is 15 kHz, as shown in FIG. 13 (b), total timeduration is used with a similar level using 8 OFDM symbols whensubcarrier spacing is 60 kHz.

Meanwhile, if a system bandwidth is wide enough and a space fortransmitting a signal is sufficiently wide, it may be able to provide atime resource for performing multi-beam transmission by using widesubcarrier spacing and generating a plurality of OFDM symbols having anarrow time interval. On the contrary, if a system bandwidth is narrow,resource allocation is performed in a frequency unit using narrowsubcarrier spacing.

3. Embodiment 3

A signal using narrow subcarrier spacing can be distinguished from asignal using wide subcarrier spacing according to a signal/channel usedfor initial access.

In this case, such a signal having narrow subcarrier spacing as aPSS/SSS/ESSS is transmitted using a long OFDM symbol and such a signalhaving wide subcarrier spacing as a BRS can be transmitted using a shortOFDM symbol.

4. Embodiment 4

When a synchronization signal or a beam measurement reference signal istransmitted using multi-beam in a massive MIMO system, duration forwhich the synchronization signal or the beam measurement referencesignal is transmitted can be restricted with a prescribed rangeirrespective of numerology. In particular, if the synchronization signalor the beam measurement reference signal is transmitted based on a longOFDM symbol, it may use the limited number of multi-beams compared to acase of transmitting the synchronization signal or the beam measurementreference signal based on a short OFDM symbol.

For example, as shown in FIG. 14, a time position of a synchronizationsignal of a numerology type 1 having long OFDM symbol duration can bematched with a time position of a synchronization signal of a numerologytype 2 having short OFDM symbol duration.

As a different example, a period of transmitting a synchronizationsignal can be configured to have the same period irrespective of an OFDMsymbol period.

FIG. 15 illustrates an example for a time period of a synchronizationsignal. FIGS. 15 (a) to (d) show an example that OFDM symbol durationfor a synchronization signal is identical or different to/from OFDMsymbol duration of a different channel Referring to FIGS. 15 (a) to (d),when there are signals and channels having various numerologies on acomponent carrier, a synchronization signal is transmitted with the sametransmission period (e.g., 5 ms).

3. Multiplexing

An NR system may have such a synchronization signal as a primarysynchronization signal (PSS), a secondary synchronization signal (SSS),and the like. As shown in FIG. 16, the signals included in thesynchronization signal can be multiplexed using a TDM or FDM scheme.

As mentioned in the following embodiments, a multiplexing scheme of aPSS/SSS can be differently applied according to numerology.

1. Embodiment 1-1

As shown in FIG. 17, TDM is performed on a PSS/SSS having long OFDMsymbol duration (e.g., 15 kHz subcarrier spacing based) and FDM isperformed on a PSS/SSS having short OFDM symbol duration (e.g., 30 kHzsubcarrier spacing based). And, assume that the PSS/SSS on which TDM isperformed has the same beam direction and the PSS/SSS on which FDM isperformed has a different beam direction.

When a PSS/SSS is transmitted on a different frequency band, amultiplexing scheme can be differently applied according to a minimumbandwidth of a channel. For example, if a system bandwidth has a limitsuch as a bandwidth less than 6 GHz, TDM is performed on a PSS/SSS. Onthe contrary, if a system bandwidth is wide such as a bandwidth widerthan 6 GHz, FDM can be performed on a PSS/SSS. Meanwhile, TDM isperformed on a PSS/SSS in a band on which a single beam is transmittedand FDM can be performed on a PSS/SSS in a band on which multi-beam istransmitted.

In case of performing multi-beam-based synchronization signaltransmission, a synchronization signal is transmitted in accordance witha direction of each beam to obtain a beamforming gain. If there are Nnumber of beams, time as much as N times of unit time for transmitting aPSS/SSS may be required. In this case, as shown in FIG. 17, one OFDMsymbol or two OFDM symbols may become the unit time for transmitting aPSS/SSS depending on a multiplexing method.

In this case, a special signal for notifying OFDM symbol positions ofrepeatedly transmitted PSSs/SSSs can be transmitted according to an OFDMsymbol in a manner of being multiplexed with a PSS/SSS.

For clarity, the special signal is referred to as an extendedsynchronization signal (ESS). Yet, a function of the ESS can be includedin a different signal depending on a design of a synchronization signal.A state to be expressed is determined according to the number of OFDMsymbols used for transmission. The state is identical to the amount ofinformation to be detected from the ESS.

2. Embodiment 1-2

On the contrary to the embodiment 1, as shown in FIG. 18, FDM isperformed on a PSS/SSS having long OFDM symbol duration (e.g., 15 kHzsubcarrier spacing based) and TDM is performed on a PSS/SSS having shortOFDM symbol duration (e.g., 30 kHz subcarrier spacing based).

For example, when PSS/SSS is multiplexed in consideration of a minimumsystem bandwidth, if a synchronization signal is transmitted bydifferentiating numerology in a system supporting various numerologies,FDM is performed on the PSS/SSS in an OFDM symbol having narrowsubcarrier spacing. On the other hand, TDM can be performed on thePSS/SSS in an OFDM symbol having wide subcarrier spacing due to abandwidth limit. When numerology is selected in accordance with a systempolicy on the same carrier or a carrier having a similar minimum systembandwidth, the abovementioned scheme can be introduced.

Meanwhile, a size of subcarrier spacing (15 kHz, 30 kHz) exemplarilymentioned in the present invention is not restrictively used. Subcarrierspacing of a different size can be applied as well.

And, although multiplexing of a PSS/SSS is described in the presentinvention as an example, the embodiments 1-1 and 1-2 can also beidentically applied to multiplexing of signals used for an initialsynchronization procedure such as an extended synchronization signal, aPBCH, a beam measurement reference signal, and the like.

3. Embodiment 1-3

FIG. 19 illustrates an example of configuring a multi-beam-basedsynchronization signal using an OFDM symbol of a different length.

Depending on OFDM symbol duration, it may be able to differentlyconfigure the number of OFDM symbols used in time domain to transmit asynchronization signal. In this case, the amount of information to bedetected by the synchronization signal can also be differentiated.Meanwhile, for example, the information to be detected by thesynchronization signal may correspond to OFDM symbol positioninformation via ESS.

Meanwhile, referring to FIG. 20, a common signal and a common channeldifferent from each other in a type can be transmitted at different timeaccording to embodiments described in the following.

1. Embodiment 2-1

When such a signal as a PSS/SSS and the like corresponds to a type-Asignal and such a signal as a PBCH/discovery RS, and the likecorresponds to a type-B signal, the type-A signal and the type-B signalcan be transmitted in a different subframe or a different OFDM symbol inthe same subframe.

2. Embodiment 2-2

Various signals can be divided into a type-A signal and a type-B signalaccording to numerology. In this case, the type-A signal using a wideOFDM symbol and the type-B signal using a narrow OFDM symbol can betransmitted to a different subframe or a different OFDM symbol in asubframe.

3. Embodiment 2-3

The type-A signal and the type-B signal designated in the embodiments2-1 and 2-2 can be multiplexed in a partial OFDM symbol in a channelincluding a different attribute.

4. Embodiment 2-4

In the embodiment 2-3, a discovery reference signal, a CSI-RS, or ameasurement RS can be configured with a short OFDM symbol and adifferent beam can be applied according to a short symbol.

4. PBCH, Beam Reference Signal

In NR system, if massive MIMO is used, the number of antenna ports canbe increased as well. In this case, it is necessary to consider a methodof obtaining maximum spatial diversity using a plurality of antennaports and a method of reducing channel estimation performancedeterioration. When a receiving end does not know the number of antennaports of a transmitting end, it is necessary to have a signal detectionmethod capable of receiving a signal without increasing receptioncomplexity.

To this end, referring to FIGS. 21 to 24, FIG. 21 and FIG. 22 illustratean example of a control channel using 4 antenna ports (APs) per unit andan example of a discovery RS using 4 antenna ports (APs) per unit,respectively. Meanwhile, FIG. 23 and FIG. 24 illustrate an example of acontrol channel using 2 antenna ports (APs) per unit and an example of adiscovery RS using 4 antenna ports (APs) per unit, respectively.

When a control channel is transmitted using a plurality of antennas in asingle OFDM, spatial diversity transmission is assumed when two or moreantenna ports are transmitted. A demodulation reference signal is sharedby the M number of antenna ports.

N numbers of frequency resource pairs near an OCC DMRS or an FDM DMRSperform spatial diversity transmission. If the N numbers of frequencyresource pairs near the DMRS resource shared by the M number of antennaports are defined as a single unit, each unit is multiplexed in afrequency unit and adjacent units are transmitted via antenna portsdifferent from each other.

Meanwhile, when data demodulation is performed, a receiving endestimates a channel using a DMRS included in a unit and restores datafrom an adjacent resource pair.

If the number of antenna ports included in a unit is less than thenumber of antenna ports of a transmitting end, a signal is transmittedusing a different antenna port between units adjacent to each other.

If the number of antenna ports included in a unit is equal to the numberof antenna ports of a transmitting end, an adjacent unit can transmit asignal using the same antenna ports. If the number of antenna portscapable of being included in a unit is greater than the number ofantenna ports of a transmitting end, a signal is transmitted using apartial resource corresponding to the number of antenna ports of thetransmitting end among DMRS resources included in the unit and anadjacent unit can transmit a signal using the same antenna port. Areceiving end assumes that a signal is transmitted using a differentantenna port between units.

In the following, embodiments of transmitting a DMRS are explained basedon the aforementioned discussion.

Embodiment 1

OCC is applied to a DMRS included in a unit using frequency domain Or,when antenna ports included in a unit are repeatedly used in a frequencyaxis, an OCC value applied to each port is changed. For example, it maybe able to cyclically select an OCC according to a port. By doing so, itis able to prevent PARR of an OFDM symbol from being increased.

Embodiment 2

A control channel demodulation reference signal is used as an RRMmeasurement RS, a CSI measurement RS, or a TRP discovery RS.

Embodiment 3

A TRP discovery RS and a control channel DMRS are configured with thesame pattern.

Embodiment 4

It may be able to configure a TRP discovery RS transmission period to bedifferent from a control channel transmission period. If thetransmissions are overlapped, a part of the TRP discovery RS is used asa DMRS of the control channel.

Embodiment 5

When a unit is configured in a unit of 4 antenna ports, OCC-4 isapplied. In this case, a sequence is mapped using 4 contiguous REs.

Embodiment 6

When a unit is configured in a unit of 4 antenna ports, SFBCtransmission is performed using two antennas and SFBC transmission isperformed in a different adjacent resource pair using another twoantennas.

Embodiment 7

In the embodiment 6, a resource pair using a different antenna can beused in an adjacent frequency resource.

Embodiment 8

In the embodiments 5 and 6, a unit uses 12 REs in total. In this case,center 4 REs are used as a DMRS and the remaining 8 REs adjacent to theDMRS are used for transmitting a control signal. In this case, SFBC isperformed using 2 RE pairs and a signal is transmitted using a differentantenna in a different adjacent resource pair. A resource can beexpanded in a scalable manner.

Embodiment 9

It is able to perform FDM on control channels having a different usage.For example, as an example of a resource including a different usage,there are a PBCH and a common control channel including a grant or atriggering message for performing paging, RAR, SIB1/2. The PBCH ispositioned at the center of an available frequency resource and thecommon control channel can be distributed to the opposite ends of afrequency.

Embodiment 10

If a unit is configured in a unit of 2 antenna ports, it may apply OCC-2and a sequence is mapped using 2 contiguous REs.

Embodiment 11

If a unit is configured in a unit of 2 antenna ports, SFBC transmissionis performed using 2 antennas. The unit can also be utilized in singleantenna transmission.

Embodiment 12

In the embodiments 10 and 11, a unit uses 6 REs in total. In this case,center 2 REs are used as a DMRS and the remaining 4 REs adjacent to theDMRS are used for transmitting a control signal. In this case, SFBC isperformed using 2 RE pairs. A resource can be expanded in a scalablemanner.

5. Beam Swept Control Channel Transmission

When a transmitting end is not precisely aware of a position of areceiving end (e.g., initial attach procedure, a user in an idle state,a user performing handover, etc.), if the transmitting end transmits acontrol channel using beamforming, beam sweeping is perform on thecontrol channel during prescribed time using multi-beam to transmit thecontrol channel.

1. Embodiment 1-1

A beam swept control channel is transmitted in a manner of beingmultiplexed with a different channel and a signal in a beam sweepingperiod.

For example, 1) the control channel can be multiplexed in an OFDM symbolincluding a PSS/SSS on which beam sweeping is performed, 2) the controlchannel can be multiplexed in an RE section, which is not used as a BRSin a BRS section in which beam sweeping is performed, or 3) the controlchannel can be multiplexed in a section in which PBCH is transmitted.

2. Embodiment 1-2

As shown in FIG. 25, a special subframe including a beam sweeping periodis defined. Beam sweeping is performed on each OFDM symbol in thespecial subframe. A control channel region and a data channel region aredefined by FDM in each OFDM symbol.

And, as shown in FIG. 26, if there is a subframe including a beamsweeping period, all or a part of OFDM symbols included in the subframecan be used for beam sweeping.

6. NR PBCH Design Target and Approach

NR system should be designed to operate on extremely differentenvironment (e.g. extremely large coverage, very high speed, wide rangeof frequency band, etc.). Also, essential information to access networkshould be delivered to any UEs. If it is desired for NR system to meetat least LTE coverage, it may design NR-PBCH based on the assumptions,which is to provide similar coding rate with LTE PBCH and to followsimilar design way (e.g. Self decoderable, Spread over multiplesubframe, Similar RS overhead).

Meanwhile, different with LTE system, NR system is operated bysingle-beam and multi-beam operation. In the multi-beam operation, beamsweeping is considering for initial access related channel/signaldelivery. On the other hand, it is desirable to limit beam sweepinginstances. So, NR could approach to use less resource elements based onassumption of less information bit size for MIB.

In the aspects above, it may provide a possible list for NR-PBCH designas follows.

1) MIB bit size: less than 40 bits (e.g. 40 bits=12 bits (information)+8bits (CRS))

2) Coded bits: 980 bits (in order to provide similar coverage with LTE)

3) Channel Coding Scheme: TBCC

4) Modulation Scheme: QPSK

5) Occupied Resource Elements (REs): 120 REs (=72×2−24)

6) Periodicity: 10 ms

7) Transmission scheme:

-   -   Option 1: Single antenna transmission scheme    -   Option 2: Transmit diversity scheme (e.g. SFBC)

8) Reference Signal:

-   -   Option 1: Self-contained DMRS    -   Option 2: Secondary Synchronization Signal    -   Note: Assume to use Cell-ID based scrambling

7. NR-PBCH Design Example

As shown in above design guide, it may assume that NR-PBCH provides 120REs, which means 24 REs can be used for DMRS within 6 RBs and 2 OFDMsymbols. Based on the assumption that adjacent two REs are used for DMRSin order to facilitate RE pairing for two antenna ports based ontransmit diversity, the NR-PBCH can be designed as shown in FIG. 27 (a)or FIG. 27 (b).

For the performance evaluation of NR-PBCH, as shown in FIGS. 28 to 31,the performance of LTE PBCH is provided as a baseline. Similar withperiodicity of LTE PBCH, assume 10 ms periodicity for NR PBCH and 4times repetition in time domain. Also, it is assumed that PBCH isself-decoderable in each subframe, and LLR combining is operated fordecoding of repeated PBCH symbol.

In this evaluation, assume that a group 1 and a group 2 for NR PBCH haveMIB bit size and time/frequency resource for PBCH transmission as below.

1) Group 1 for NR PBCH:

-   -   12 RBs with 2 symbols for 40 bits    -   6 RBs with 2 symbols for 20 bits

Group 2 for NR PBCH

-   -   24 RBs with 2 symbols for 40 bits    -   12 RBs with 2 symbols for 20 bits

Group 1 for NR PBCH design has similar coding rate with LTE PBCH. On theother hand, twice time/frequency resources are assigned for Group 2 forNR PBCH. In this simulation, 2Tx SFBC is assumed with same DMRS overheadfor both LTE PBCH and NR PBCH.

In FIGS. 28 and 29, PBCH performances are shown according to wirelesschannel environment. Referring to FIGS. 28 and 29, Group 1 (NR designwith same overhead of LTE PBCH) has performance degradation due tochannel estimation performance loss. When same DRMS overhead with LTEPBCH is considered, it is shown that more time/frequency resources forNR PBCH transmission are necessary to meet similar PBCH coverage withNR.

FIG. 30 shows PBCH performance with residual frequency offset afterfrequency offset estimation using synchronization signal in initialaccess. In the simulation, it may assume 1.5 kHz frequency offset whichis about 10% of SCS 15 kHz.

From the simulation result, it may observe that NR PBCH design couldoperate at the case with residual frequency offset. It shows apossibility that self-contained DMRS at first OFDM symbol in NR PBCHcould be used for data demodulation of 2^(nd) OFDM symbol withoutresidual frequency offset compensation.

FIG. 31 shows PBCH performance comparison for PBCH design between singleOFDM symbol and two OFDM symbols.

In FIG. 31, assume maximum 5 MHz bandwidth for PBCH transmission and 24RBs are assigned for 1 symbol based PBCH transmission. If 24 RBs with 1symbol for 40 bits is compared with 24 RBs with 2 symbols for 40 bits,about 2.5 dB performance gap is observed. Also, compared with LTEdesign, 1 symbol based design shows about 2 dB performance loss. So, itmay observe that when maximum 5 MHz bandwidth is assumed for PBCHtransmission, 1 symbol based PBCH design is not enough to achieve therequired coverage.

As a different example, NR PBCH can be configured by a single OFDMsymbol. In this case, it may assume a DMRS per port according to eachRB. In this case, although it is able to lower a coding rate used fortransmitting PBCH, channel estimation capability via a DMRS can bedegraded. In order to enhance the channel estimation capability, it mayassign an additional DMRS. For example, 2 REs per port can be configuredas a DMRS according to an RB.

8. Multiplexing of NR-SS and NR-PBCH

NR-PSS, NR-SSS and/or NR-PBCH can be transmitted in a manner of beingincluded in an SS block. TDMed SS has a benefit in terms of lowercomplexity of timing detection and faster acquisition for Cell-IDcompared to FDMed SS. Based on the assumption that NR-PSS and NR-SSS areTDMed, it may consider three alternatives for composition of NR-SS andNR-PBCH as follows.

1) Option 1: NR-SS and NR-PBCH are TDMed. In this case, NR-SS andNR-PBCH have same bandwidth.

2) Option 2: NR-SS and NR-PBCH are TDMed. In this case, NR-PBCH haswider bandwidth.

3) Option 3: NR-SS and NR-PBCH are FDMed.

FIGS. 32 (a), (b), and (c) show composition of NR-SS and NR-PBCHaccording to the options, 1, 2, and 3.

For option 1, same bandwidth is assumed for NR-PSS, NR-SSS and NR-PBCH,where longer time duration is required for NR-PBCH transmission. Foroption 2, it is assumed that NR-PBCH has wider bandwidth than NR-SS,where NR-PBCH can obtain frequency diversity gain. For option 3, twoOFDM symbols are assigned for ‘SS block’, where NR-PBCH is located atadjacent subbands.

Considering on the assumption to use 15 kHz or 30 kHz subcarrier spacingfor below 6 GHz, three options shows that transmission bandwidthcontaining NR-SS/NR-PBCH is not exceed 5 MHz. For design commonality,these options could be applied to below 40 GHz. If 120 kHz or 240 kHzsubcarrier spacing of ‘SS block’ is assumed for below 40 GHz, threeoptions shows that transmission bandwidth containing NR-SS/NR-PBCH isnot exceed 40 MHz.

In order to keep detection complexity for NR-PSS and provide robustnessagainst frequency offset in initial detection step, it can be assumedthat NR-PSS and NR-SSS have same bandwidth, but NR-PSS subcarrierspacing is wider than NR-SSS. Also, in order to facilitate same FFT sizefor NR-SSS and NR-PBCH, it can be assumed that NR-PBCH subcarrierspacing is same with NR-SSS subcarrier spacing.

9. SS Bandwidth and Multiplexing

Transmission bandwidth for synchronization signal is related with UEdetection complexity. If the transmission bandwidth becomes wider,sampling rate for synchronization signal transmission and reception isalso increased. As a result, synchronization signal detection complexityof UE side increases as well. Two factors (i.e. subcarrier spacing andmultiplexing method for SS) can be considered as a main element whichtransmission bandwidth becomes wider. If wider subcarrier spacing isintroduced for robustness against frequency offset, transmissionbandwidth could be also linearly increased.

Also, if synchronization signals are FDMed, transmission bandwidth isincreased by twice. However, if it is not preferred to increase UE sidedetection complexity according to wider transmission bandwidth, it mayconsider possible solutions (e.g. new sequence design for NR,multiplexing of synchronization signals in time domain, etc.) to preventincreasing transmission bandwidth.

In legacy LTE specification, the bandwidth for synchronization signal isdefined as 1.08 MHz, and the OFDM symbol duration is defined as 70 μs.In the present invention, it may provide new PSS design which hassimilar transmission bandwidth with LTE and wider subcarrier spacing(i.e. 60 kHz). Also, in the present invention, time domain multiplexingis assumed for NR SS.

From the simulation result, it may observe the possibility that NR SSsequence provides a better performance than LTE SS sequence even inlarger frequency offset, and detection complexity for synchronization isnot higher than LTE SS detection.

In this point of view, it may consider the NR SS design thattransmission bandwidth for NR synchronization signal is similar withthat of LTE for below 6 GHz, and synchronization signals are multiplexedin time domain. Also, considering on linear scaling of transmissionbandwidth according to subcarrier spacing, N (e.g. N is four) timeswider transmission bandwidth can be applied for below 40 GHz band.

For initial access, NR assumes both single-beam and multi-beamtransmission. Especially, for multi-beam transmission, beam sweeping isconsidered as a possible approach. Considering on beam sweeping forsynchronization signals, there is a possible issue related withmultiplexing of SS and PBCH.

One way of multiplexing of SS and PBCH is TDMed within contiguous OFDMsymbols as shown in FIG. 33. For single beam case, this method lookssimilar with multiplexing LTE SS and LTE PBCH. For multi-beam case, beamis swept at every N OFDM symbols, which is a time unit for multiplexingof NR SS and NR PBCH.

However, in case that transmission periodicity for NR SS and NR PBCH isdifferent, the time period for OFDM symbols of NR PBCH transmissioncould be reserved for beam sweeping even in NR PBCH is not transmitted.In order to resolve the ambiguity of the time period, it can beconsidered that NR SS and NR PBCH are transmitted with timing gap (e.g.0.5 ms) as shown in FIG. 34.

In FIG. 34, it is described that time domain multiplexed synchronizationsignals are transmitted using same beam direction within contiguous twoOFDM symbols, and analog beam is changed at every two OFDM symbols.Also, beam sweeping is operated within timing gap (e.g. 0.5 ms). When NRPBCH is constructed by two OFDM symbols, same beam sweeping operation ofNR SS could be assumed for NR PBCH. After NR synchronization signal isdetected, UE can expect to receive NR PBCH which has same beam directionwithin timing gap. If NR PBCH is not transmitted, the time resourcecould be assigned for other channel/signal transmission.

10. Frequency Raster

The raster for NR synchronization signals can be different per frequencyrange. At least for frequency ranges where NR supports a wider carrierbandwidth and operation in a wider frequency spectrum (e.g. above 6GHz), the NR synchronization signals raster can be larger than the 100kHz raster of LTE.

If NR SS is multiplexed in time domain, it may define that the centerfrequency of synchronization signals is same with the center oftransmission bandwidth of SS block. In the present invention, an exampleof time domain multiplexing for NR SS and NR PBCH within SS block isprovided. In this case, it may assume same multiplexing method for bothbelow 6 GHz and below 40 GHz. In particular, as shown in FIG. 35, commondefinition for center frequency of synchronization signal is applied forboth frequency ranges.

In FIG. 35, UE can assume that both NR synchronization signal and NRPBCH are transmitted at the center frequency of the NR SS block. Basedon this assumption, UE can operate synchronization signal detection andPBCH decoding, which are multiplexed in time domain.

On the other hand, if NR SS is multiplexed in frequency domain, it maydefine that the center frequency of NR SS transmission bandwidth whichis required for both NR PSS and NR SSS is same with the center oftransmission bandwidth of SS block as shown in FIG. 36. Furthermore, ifPBCH is multiplexed with synchronization signals in frequency domain, itcould be possible that PBCH is located at each adjacent frequency bandfrom end of SSS and PSS.

In NR, center of synchronization signal or SS transmission bandwidth canbe different from the center of NR carrier. However, for at leastinitial access, it is needed that UE can operate synchronization signaldetection and PBCH demodulation within SS block without any informationregarding the position of synchronization signal in NR carrier.Meanwhile, the position of the center of synchronization signal in NRcarrier can be indicated for intra frequency/inter frequencymeasurement.

In an NR system supporting a broadband bandwidth, a channel including asynchronization signal and information required for initial access canbe transmitted on a relatively narrow band. A UE attempting to performinitial access assumes a narrow band including a synchronization signaland an initial access channel as a base bandwidth for reception todetect a signal and obtains information for accessing a cell. The basebandwidth may correspond to a minimum bandwidth capable of beingtransmitted by a base station. For example, LTE defines 1.4 MHz as aminimum bandwidth and maximum 20 MHz bandwidth can be supported on asingle carrier. Meanwhile, in the NR system, a minimum bandwidth can bedefined by 5 MHz in a band equal to or less than 6 GHz and can bedefined by 20 MHz in a band equal to or less than 6 GHz.

If a minimum bandwidth is assumed, a UE is able to search for asynchronization signal and obtain minimum system information. Theminimum system information can include a system bandwidth used for a UEto perform initial access and measurement. In this case, it is assumedthat a center frequency of the minimum bandwidth is identical to acenter frequency of the system bandwidth. In this case, the centerfrequency may not be matched with a center frequency of NR carrier. Achannel required for initial access, a reference signal for performingmeasurement, and the like can be assigned on the basis of the centerfrequency of the minimum bandwidth and the system bandwidth. Forexample, it may be able to assume that a center frequency of asynchronization signal is identical to the center frequency of theminimum bandwidth and a center value of indexes of subcarriers used inthe system bandwidth is identical to a position of the center frequencyof the system bandwidth. An index used in the system bandwidth can beconsidered as a local index used in a corresponding band only. In NRcarrier, a plurality of system band (or synchronization signal blockbandwidth) candidates including a synchronization signal may exist. Itis able to manage a frequency index such as a subcarrier and the likeusing a local index in each of a plurality of the system bandcandidates. In the NR carrier, it may be able to assume that a pluralityof synchronization signals can be transmitted on a different band. A UEattempts to detect a synchronization signal in an initial access step.In this case, the UE assumes a possibility capable of detectingsynchronization signals on other bands. If a plurality ofsynchronization signals are detected, the UE assumes a plurality of thedetected synchronization signals as an independent cell or atransmitting end and performs synchronization procedure and a cellaccess procedure. If minimum system information forwards information oncell access, NR can inform a UE of a band on which the cell accessprocedure is permitted among a plurality of bands.

NR system can variably manage a period of a synchronization signal fornetwork energy saving. If a UE does not know a transmission periodprovided by a network, the UE performs synchronization signal detectionby assuming default periodicity.

If a synchronization signal is transmitted with a periodicity slowerthan the periodicity assumed by the UE, synchronization signal detectioncapability of the UE is considerably deteriorated. In order to preventthe capability deterioration, at least one or more transmitting ends cantransmit a channel including a synchronization signal and initialaccess-related information with the default periodicity assumed by theUE. In NR carrier having a broad bandwidth, a plurality ofsynchronization signals can be transmitted. In this case, at least oneor more carriers among a plurality of the synchronization signals assumethat a synchronization signal is transmitted with the defaultperiodicity of the UE.

If a synchronization signal is transmitted with a periodicity longerthan the default periodicity assumed by the UE, it may not transmit thechannel including the information for initial access. In this case, asynchronization signal and an RS for performing measurement aretransmitted to enable an NR cell to perform measurement even in a longperiod.

11. SS Block Composition

If payload size of PBCH is up to 80 bits, it may assume that total fourOFDM symbols are occupied for SS block transmission. Then it isnecessary to discuss the time position of NR-PSS/NR-SSS/NR-PBCH withinSS block where NR-PSS, NR-SSS and NR-PBCH are presented. In initialaccess state, NR-PBCH can be used as reference signal for finetime/frequency tracking. In order to enhance the estimation accuracy, itis better that two OFDM symbols for NR-PBCH are located with longerdistance. In this aspect, as shown in FIG. 37 (a), it is proposed that1^(st) and 4^(th) OFDM symbols of SS block are used for NR-PBCHtransmission. Also, it can be assumed that 2^(nd) OFDM symbol isassigned for NR-PSS, and 3^(rd) OFDM symbol is occupied for NR-SSS.

Meanwhile, when NR-SS is transmitted for the purpose of cell measurementor cell discovery, it could be not necessity to transmit both NR-PBCHand SS block time index indication. In this case, as shown in FIG. 37(b), SS block is composed by two OFDM symbols, where 1^(st) OFDM symbolis assigned for NR-PSS and 2^(nd) OFDM symbol is used for NR-SSS.

Referring to FIG. 38 (a), NR-PBCH is allocated within 288 REs, which is24 RBs. On the other hand, it is decided that the sequence forNR-PSS/NR-SSS has the length of 127, hence it can be assumed that 12 RBsare required for NR-PSS/NR-SSS transmission. For SS block composition,we can define that SS block is allocated within 24 RBs. Also, the valueof 24 RB is appropriate for RB grid alignment between differentnumerologies (e.g. 15, 30, 60 kHz). Even NR assumes minimum bandwidth of5 MHz where 25 RBs for 15 kHz subcarrier spacing can be defined, itshould be assumed that 24 RBs are used for SS block transmission. Also,it should be defined that NR-PSS/SSS is located at middle of SS Block,which means that NR-PSS/SSS are allocated within 7^(th) to 18^(th) RBs.

Meanwhile, NR-PSS/NR-SSS/NR-PBCH can be assigned as shown in FIG. 38(b). In particular, NR-PSS is assigned to a symbol #0 and NR-SSS can beassigned to a symbol #2. And, NR-PBCH can be assigned to symbols #1 to#3. In this case, the symbol #1 and the symbol #3 may correspond todedicated symbols to which the NR-PBCH is mapped. In particular, onlythe NR-PBCH is mapped to the symbol #1 and the symbol #3 and the NR-SSSand the NR-PBCH can be mapped to the symbol #2 together.

12. SS Burst Composition

In the present invention, it is necessary to verify which OFDM symbolsare available to transmit SS Block within a slot. A CP type can besemi-statically configured with UE-specific signaling. Also, NR-PSS/SSScan support a normal CP. So, CP detection issue can be eliminated ininitial access.

In the NR system, NR can include an extended CP at every 0.5 msboundary. When SS block is located within a slot or across inter-slot,it could be possible that middle of SS Block is located at 0.5 msboundary. In this case, different length of CP among NR-PSS/SSS isapplied within a SS Block. If UE operates NR-SS detection based on theassumption that normal CP is applied for NR-PSS/SSS, detectionperformance could be degraded. So, NR should consider that SS block isnot located across 0.5 ms boundary.

FIG. 39 illustrates an example of SS burst composition for TDD case. InNR, DL control channel(s) is located at the first OFDM symbol(s) in aslot and/or mini slot, and UL control channel(s) is located around thelast transmitted UL symbol(s) of a slot. In order to avoid a collisionof SS Block and DL/UL control channel, SS block can be located in themiddle of slot.

The maximum number of SS blocks within SS burst set is decided accordingto frequency ranges. Also, candidate values of SS blocks are determinedaccording to frequency ranges. Meanwhile, based on the example of SSburst composition in FIG. 39, the present invention proposes overalltime duration to transmit SS blocks within SS burst set.

TABLE 1 The maximum number of SS block Subcarrier Spacing 1 2 4 8 32 64 15 kHz 1 ms   1 ms 2 ms 4 ms — —  30 kHz — 0.5 ms 1 ms 2 ms — — 120 kHz— — — — 2 ms 4 ms 240 kHz — — — — 1 ms 2 ms

As shown in Table 1, if subcarrier spacing of 30 kHz and 240 kHz areintroduced for NR-SS transmission, it can be expected that the SS blocksare transmitted within maximum 2 ms. However, since 15 kHz and 120 kHzare default subcarrier spacing for NR-SS transmission, in order tointroduce the subcarrier spacing of 30 kHz and 240 kHz, it is necessaryto discuss whether or not to introduce wider minimum system bandwidth(i.e. 10 MHz for 30 kHz subcarrier spacing, 80 MHz for 240 kHzsubcarrier spacing). If it is decided that NR supports only minimumsystem bandwidth of 5 MHz for below 6 GHz and 50 MHz for above 6 GHz, itis necessary to design SS burst set based on 15 kHz and 120 kHzsubcarrier spacing. If it is assumed that the maximum number of SS Blockis 8 for below 6 GHz and 64 for above 6 GHz, required time for SS Blocktransmission is 4 ms, which seems quite large system overhead. Also,because short duration is preferable for network energy saving and UEmeasurement perspective, it should be assumed that candidate position ofassignment for SS block transmission is defined within N ms timeduration (e.g N=0.5, 1, 2).

13. SS Burst Set Composition

For the SS burst set composition, it may consider two types according toperiodicity of SS burst occasion as shown in FIG. 40. The localized typeshown in FIG. 40 (a) is that all the SS block is contiguouslytransmitted within the SS burst set, while the distributed type shown inFIG. 40 (b) is that SS burst is periodically transmitted within the SSburst set periodicity.

In the perspective of energy saving for IDLE UE and efficiency forinter-frequency measurement, the localized type of SS burst occasionprovides the benefit compared with the distributed type of SS burstoccasion. In this case, it would seem preferable to support thelocalized type of SS burst occasion.

For initial access, NR can consider that candidate position for SS blocktransmission within SS burst set periodicity is specified. Also, theposition(s) of actual transmitted SS Blocks can be informed forCONNECTED/IDLE mode UE. In this case, network can have a flexibility toutilize resource according to the network condition. However, accordingto the configuration method to inform actually used SS Block,flexibility to compose SS burst set could be different. For example, ifthe individual position information of actual transmitted SS Blocks(e.g. bitmap for SS Block or SS burst) can be configured to UE, bothlocalized type and distributed type could be operated according tonetwork condition. This information can be included in other SI whichindicates measurement related information.

SS burst set periodicity can be changed and the information ofmeasurement timing/duration for UE can be provided by networkconfiguration. However, it is necessary to determine the candidateposition of SS block transmission when SS burst set periodicity ischanged. In the present invention, two embodiments are proposed todetermine the position of SS block transmission.

Embodiment 1

Network uses the candidate position assumed for default periodicity.

Embodiment 2

Network indicates the actual position to transmit SS-blocks withinmeasurement duration.

In particular, NR can design SS burst set composition for defaultperiodicity. Also, when SS burst set periodicity and measurementduration are indicated by network, the SS burst set composition could beassumed for SS block configuration. For example, if UE assumes 5 msperiodicity as the SS burst set periodicity for measurement in case ofno indication from network, it is necessity to compose SS burst set for5 ms periodicity. Also, the SS burst set composition can be also usedfor the case of default periodicity (e.g. 20 ms) and network configuredperiodicity (e.g. 5, 10 20, 40, 80, 160 ms).

On the other hand, if more efficient resource utilization for SS burstset composition is considered, network can indicate the actual positionto transmit SS-blocks within measurement duration. For example, in thecase of default periodicity, NR-SS and NR-PBCH should be transmittedwithin SS burst set periodicity. On the other hand, in the case oflonger periodicity, only NR-SS could be transmitted for measurementpurpose. If network can configure the actual position for SS blocktransmission, unused resource assigned for NR-PBCH can be assigned fordata/control channel. Also, in the case of short periodicity, networkselects some part of SS block among SS blocks within SS burst set, andcan configure the actually used SS block.

14. Signal/Channel for Time Index Indication

SS block time index indication is delivered by NR-PBCH. If the timeindex indication is contained at a part of NR-PBCH (e.g. NR-PBCHcontents, scrambling sequence, CRC, Redundancy Version, etc.), it has anadvantage that indication is securely delivered to UE. However, itbrings additional complexity of decoding of neighbor cell NR-PBCH.Meanwhile, decoding of NR-PBCH for neighbor cell would be possible, butthis cannot be mandated for system design. Also, it is necessary to havefurther discussion on which signal and channel is appropriate to deliverthe SS block time index indication.

In the target cell, the SS block time index information should besecurely delivered to UE since the index will be used as the referenceinformation of time resource designation for initial access relatedchannel/signal (e.g. system information delivery, PRACH preambleoccasion, etc.). On the other hand, for the purpose of neighbor cellmeasurement, the time index is used for SS block level RSRP measurement.In this case, highly accurate acquisition performance may not benecessity.

The present invention proposes that NR-PBCH DMRS is used as a signal todeliver SS block time index. Also, the present invention proposes thatthe time index indication should be included at a part of NR-PBCH. Usingthis solution, SS block time index can be detected from NR-PBCH DMRS.Then, the detected index can be confirmed by NR-PBCH decoding. And, forthe neighbor cell measurement, the index can be obtained from NR-PBCHDMRS for neighbor cell.

The time index indication can be configured by two embodiments in thefollowing.

Embodiment 1

Single index method (i.e. one time index for every SS-block within anSS-burst set)

Embodiment 2

Multiple index method (i.e. combination of SS burst index and SS blockindex)

If single index method is supported, large number of bits is necessityto express the all possible number of SS blocks within SS burst setperiodicity. In this case, DMRS sequence and scrambling sequence forNR-PBCH are preferable to indicate SS block indication.

On the other hand, if multiple index method is applied, the designflexibility for index indication could be provided. For example, both SSburst index and SS block index can be included in single channel. Also,each index can be separately transmitted via different channel/signal.For example, SS burst index is included in NR-PBCH (e.g. contents,scrambling sequence), and the SS block index is delivered by DMRSsequence for NR-PBCH.

15. SS Block Time Index

The present invention proposes that SS burst set is composed withinshorter duration (e.g. 2 ms) for network and UE energy saving. In thiscase, all of SS blocks can be located within SS burst set periodicityregardless of the value of periodicity (e.g. 5, 10, 20, 40, 80, 160 ms).FIG. 41 shows an example of SS block index for the case of 15 kHzsubcarrier spacing.

SS block index is explained with reference to FIG. 41. If the maximumnumber of SS block is defined as L, the index of SS block is from 0 toL−1. Also, the SS block index is derived from OFDM symbol index and slotindex. In this case, SS burst set is composed by four SS blocks, whichis located at contiguous two slots. So, the index of SS block is from 0to 3, and the index of slot is 0 and 1. Also, SS block is composed byfour OFDM symbols, and two OFDM symbols within SS block are used forPBCH transmission. In this case, the index of OFDM symbol is 0 and 2. Asshown in FIG. 41 (a), the index of SS block is derived from the index ofOFDM symbol and slot. For example, the SS block transmitted at slot#1and OFDM symbol#2 is mapped to index of 3.

In NR, network can configure the periodicity of SS burst set. Also,shorter periodicity (i.e. 5, 10 ms) can be configured. In this case,more occasions can be assigned for SS block transmission. The index ofSS block is identified within configured periodicity of SS burst set. Asshown in FIG. 41 (c), in case of 5 ms periodicity, four SS blocks can betransmitted within configured periodicity, and total 16 SS blocks aretransmitted within default periodicity. In this case, the index of SSblock could be repeated within default periodicity, and four SS blocksamong 16 SS blocks have same index.

16. NR-PBCH Contents

Based on the response LS from RAN2, it is expected that the payload sizeof MIB can be extended a bit. Payload size of MIB and NR-PBCH contentsexpected in NR are as follows.

1) Payload: 64 bits (48 bits information, 16 bits CRC)

2) NR-PBCH Contents:

-   -   At least part of SFN/H-SFN    -   Configuration information for common search space    -   Center frequency information of NR carrier

17. Transmission Scheme and Antenna Port

In NR system, NR-PBCH transmission is performed based on single antennaport. For the single antenna port based transmission, it may considerfollowing embodiments as a scheme for NR-PBCH transmission.

Embodiment 1

Time domain precoding vector switching (TD-PVS) scheme

Embodiment 2

Cyclic Delay Diversity (CDD) scheme

Embodiment 3

Frequency domain precoding vector switching (FD-PVS) scheme

According to the transmission scheme, NR-PBCH can achieve transmitdiversity gain and/or channel estimation performance gain. TD-PVS andCDD can be considered as candidate of NR-PBCH transmission. On the otherhand, FD-PVS is not preferable, because overall performance loss isappeared due to channel estimation loss.

Also, antenna port assumption for NR-SS and NR-PBCH is explained. Ininitial access state, it is quite natural that NR can consider differentantenna port of NR-SS and NR-PBCH in order to provide networkflexibility for NR-SS and NR-PBCH transmission. On the other hand, ifnetwork configuration is defined, UE can assume that antenna port ofNR-SS and NR-PBCH is same or different.

18. NR-PBCH DM-RS Design

In NR system, DMRS is introduced for phase reference of NR-PBCH. Also,NR-PSS/NR-SSS/NR-PBCH are presented in every SS block, and OFDM symbolsin a single SS block are consecutive. However, if it is assumed thattransmission scheme is different between NR-SSS and NR-PBCH, it cannotbe assumed that NR-SSS is used as reference signal for NR-PBCHdemodulation. Instead, NR should design NR-PBCH based on the assumptionthat NR-SSS is not used as reference signal for NR-PBCH demodulation.

For the DMRS design, it is necessary to consider DMRS overhead,time/frequency position and scrambling sequence.

Overall PBCH decoding performance can be determined by channelestimation performance and NR-PBCH coding rate. Since the number of REfor DMRS transmission has a trade-off between channel estimationperformance and PBCH coding rate, it is necessary to find theappropriate number of RE for DMRS. For example, when 4 REs per RB isassigned for DMRS, better performance can be provided. When two OFDMsymbols are assigned for NR-PBCH transmission, 192 REs for DMRS and 384REs for MIB transmission are used. In this case, when 64 bits of payloadsize is assumed, 1/12 coding rate can be achieved, which is same codingrate with LTE PBCH.

When multiple OFDM symbols are assigned for NR-PBCH transmission, it isnecessary to discuss which OFDM symbol contains DMRS. It is preferablethat DMRS is located at every OFDM symbol for NR-PBCH to preventperformance degradation due to residual frequency offset. So, each OFDMsymbol for NR-PBCH transmission can include DMRS.

For the OFDM symbol position for NR-PBCH transmission, PBCH DMRS is usedas fine time/frequency tracking RS. When longer time distance betweentwo OFDM symbols including DMRS is assumed, it is more beneficial forfine frequency tracking. Hence, 1^(st) and 4^(th) OFDM symbols can beassigned for NR-PBCH transmission.

Also, regarding on frequency position of DMRS, it may assume theinterleaved mapping in frequency domain, which can be shifted accordingto cell-ID. Equally distributed DMRS pattern could have benefit to useDFT based channel estimation which provides optimal performance in caseof 1-D channel estimation. Also, in order to increase channel estimationperformance, wideband wide RB bundling can be used.

For sequence of DMRS, pseudo random sequence defined by a type of Goldsequence can be introduced. The length of DMRS sequence can be definedby the number of RE for DMRS per SS block. Also, the DMRS sequence canbe generated by cell-ID and slot number/OFDM symbol index within defaultperiodicity of SS burst set (i.e. 20 ms). Also, the index of SS blockcan be determined based on the index of slot and OFDM symbol.

19. NR-PBCH TTI Boundary Indication

NR-PBCH TTI is 80 ms, and default periodicity of SS burst set is 20 ms.It means that NR-PBCH is transmitted four times within NR-PBCH TTI. WhenNR-PBCH is repeated within NR-PBCH TTI, TTI boundary indication isnecessity. Similar with LTE PBCH, NR-PBCH TTI boundary can be indicatedby scrambling sequence of NR-PBCH.

Also, referring to FIG. 42, the scrambling sequence of NR-PBCH can bedetermined by cell-ID and TTI boundary indication. Because multiplevalues of SS burst set periodicity are supported, the number of indexfor TTI boundary indication can be changed according to SS burst setperiodicity. For example, four indices are required for defaultperiodicity (i.e. 20 ms), and 16 indices are necessity for shorterperiodicity (i.e. 5 ms).

Meanwhile, NR system supports both single beam transmission andmulti-beam transmission. When multiple SS blocks are transmitted withinSS burst set periodicity, SS block index can be assigned to each of theSS blocks. For the randomization between SS blocks for inter-cell,scrambling sequence should be determined by an index related with SSblock. For example, if the index of SS block is derived from the indexof slot and OFDM symbol, it can be considered that scrambling sequenceof NR-PBCH is determined by the index of slot and OFDM symbols.

If network configures shorter periodicity of SS burst set (i.e. 5, 10ms), more occasion for SS burst set transmission would be assigned. Inthis case, UE may have ambiguity regarding the TTI boundary of NR-PBCHswhich are transmitted within default periodicity. For NR-PBCH TTIboundary indication for shorter periodicity, it may consider a differentscrambling sequence of NR-PBCH for shorter periodicity. For example, if5 ms of periodicity of SS burst set is assumed, 16 scrambling sequencesfor NR-PBCH are applied. It may have a benefit to indicate the exactboundary of NR-PBCH transmission within NR-PBCH TTI. On the other hand,blind detection complexity for NR-PBCH decoding is increased. In orderto reduce the blind decoding complexity of NR-PBCH, it may introducedifferent NR-SSS sequence for shorter periodicity in order todistinguish NR-SSS with default periodicity from additionallytransmitted NR-SSS within default periodicity.

20. Soft Combining

NR should support wise soft combining to at least SS burst set toprovide efficient resource utilization and PBCH coverage. Since NR-PBCHis updated every 80 ms and SS burst set is transmitted every 20 ms ofdefault periodicity, at least four times soft combining is possible forNR-PBCH decoding. Also, when shorter periodicity of SS burst set isindicated, more OFDM symbols for PBCH can be used for soft combining.

21. PBCH Decoding for the Neighboring Cell Measurements

For the neighbor cell measurement, it has to be decided whether the UEhas to decode NR-PBCHs of neighboring cells. Decoding of neighboringcells would increase the UE complexity and it would be better not toincrease unnecessary complexity. Therefore, for NR-PBCH design, itshould be assumed that UE does not need to decode neighbor cell NR-PBCHfor neighbor cell measurement.

On the other hand, if SS block index is delivered by a signal of aspecific type, UE can obtain the SS block index of neighbor cells byperforming signal detection operation, which could provide a benefit ofless complexity. As the signal of the specific type, NR-PBCH DMRS can beconsidered.

22. Performance Evaluation

In the present section, a performance result is explained according topayload size, a transmission scheme and a demodulation reference signal.In this evaluation, assume that two OFDM symbols with 24 RBs are usedfor NR-PBCH transmission. Also, it is assumed that multiple periodicityof SS burst set (i.e. 10, 20, 40, 80 ms) is assumed, and encoded bitsare transmitted within 80 ms.

1. Payload Size and NR-PBCH Resource

FIG. 43 provides evaluation result according to MIB payload size (i.e.64, 80 bits). In this evaluation, assume that 384 REs for informationand 192 REs for DMRS are used within two OFDM symbols and 24 RBs. Also,single antenna port based transmission scheme (i.e. TD-PVS) is assumed.

Referring to FIG. 43, it is able to observe that NR-PBCH with 20 msperiodicity can provide 1% error rate at −6 dB SNR. Also, it is observedthat performance of 64 bits of payload case have 0.8 dB gain than thatof 80 bits of payload case. So, if payload size between 64 bits and 80bits is assumed, the performance requirement of NR-PBCH (i.e. 1% BLER at−6 dB SNR) can be satisfied using 24 RBs and two OFDM symbols.

2. Transmission Scheme

FIG. 44 provides evaluation result according to NR-PBCH transmissionschemes (i.e. TD-PVS and FD-PVS). Note that precoders are cycled inevery PBCH transmission subframe (e.g. 20 ms) for TD-PVS and every N RBs(e.g. N is 6) for FD-PVS. Also, in FIG. 44, assume several periodicityof SS burst set (i.e. 10, 20, 40, 80 ms), and soft combining of NR-PBCHacross SS burst set within 80 ms.

As shown in FIG. 44, Time-Domain Precoding Vector Switching (TD-PVS)scheme shows better performance than Frequency-Domain Precoding VectorSwitching (FD-PVS) due to better channel estimation performance. In thisevaluation, it is able to see that channel estimation performance ismore important than transmit diversity gain in very low SNR region.

3. DMRS Density

At the low SNR region, channel estimation performance enhancement is animportant factor for demodulation performance enhancement. However, whenRS density of NR-PBCH is increased, the channel estimation performanceis improved, but coding rate is decreased. So, in order to see thetrade-off between channel estimation performance and channel codinggain, the decoding performances are compared with each other accordingto DMRS density. FIG. 45 illustrates an example of the DMRS density.

FIG. 45 (a) shows a case that 2 REs per symbol are used for DMRS, FIG.45 (b) shows a case that 4 REs per symbol are used for DMRS, and FIG. 45(c) shows a case that 6 REs per symbol are used for DMRS. Note thatsingle port based transmission scheme (i.e. TD-PVS) is used for thisevaluation.

FIG. 45 shows DMRS pattern for single antenna port based transmission.Referring to FIG. 45, DMRS position in frequency domain is changedaccording to RS density, which keeps equal distance between referencesignals. Also, in FIG. 46, it shows performance result according toreference signal density of DMRS.

As shown in FIG. 46, NR-PBCH decoding performance shown in FIG. 45 (b)is better than performance shown in FIG. 45 (a) because of betterchannel estimation performance. On the other hand, FIG. 45 (c) showsworse performance than FIG. 45 (b), because the effect of the codingrate loss is greater than the gain of channel estimation performanceenhancement. Due to the aforementioned reasons, 4 RE per symbol seemsproper point of RS density.

4. DMRS Time Position and CFO Estimation

If NR supports self-contained DMRS, it is able to perform fine frequencyoffset tracking on NR-PBCH using self-contained DMRS. Since frequencyoffset estimation accuracy depends on the OFDM symbol distance, it mayassume three types of NR-PBCH symbol spacing as shown in FIG. 47.

This simulation is performed on SNR −6 dB, and 10% CFO (1.5 kHz) isapplied over samples in a subframe. 4 REs per symbol are used asself-contained RS, and located on the symbols where PBCH is transmitted.

FIGS. 48 and 49 show CDF of estimated CFO according to different NR-PBCHsymbol spacing. As shown in FIGS. 48 and 49, CFO of 1.5 kHz is wellestimated within error of ±200 Hz by 90% of UEs in both cases, and if atleast 2 symbols are introduced as NR-PBCH symbol spacing, 95% of UEsshows error within ±200 Hz, and 90% of UEs shows error within ±100 Hz inboth cases.

CFO estimation performance is better when the spacing between PBCHsymbols is larger, because phase offset caused by the CFO grows large asspacing increase, making easy to measure phase offset with similareffect as noise suppression. Also, large average window helps theaccuracy of CFO estimation.

FIG. 50 is a block diagram of a communication apparatus according to anembodiment of the present disclosure.

Referring to FIG. 50, a communication apparatus 5000 includes aprocessor 5010, a memory 5020, an RF module 5030, a display module 5040,and a User Interface (UI) module 5050.

The communication device 5000 is shown as having the configurationillustrated in FIG. 50, for the convenience of description. Some modulesmay be added to or omitted from the communication apparatus 5000. Inaddition, a module of the communication apparatus 5000 may be dividedinto more modules. The processor 5010 is configured to performoperations according to the embodiments of the present disclosuredescribed before with reference to the drawings. Specifically, fordetailed operations of the processor 5010, the descriptions of FIGS. 1to 49 may be referred to.

The memory 5020 is connected to the processor 5010 and stores anOperating System (OS), applications, program codes, data, etc. The RFmodule 5030, which is connected to the processor 5010, upconverts abaseband signal to an RF signal or downconverts an RF signal to abaseband signal. For this purpose, the RF module 5030 performsdigital-to-analog conversion, amplification, filtering, and frequencyupconversion or performs these processes reversely. The display module5040 is connected to the processor 5010 and displays various types ofinformation. The display module 5040 may be configured as, not limitedto, a known component such as a Liquid Crystal Display (LCD), a LightEmitting Diode (LED) display, and an Organic Light Emitting Diode (OLED)display. The UI module 5050 is connected to the processor 5010 and maybe configured with a combination of known user interfaces such as akeypad, a touch screen, etc.

The embodiments of the present invention described above arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions of any oneembodiment may be included in another embodiment and may be replacedwith corresponding constructions of another embodiment. It is obvious tothose skilled in the art that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim by asubsequent amendment after the application is filed.

A specific operation described as performed by a BS may be performed byan upper node of the BS. Namely, it is apparent that, in a networkcomprised of a plurality of network nodes including a BS, variousoperations performed for communication with a UE may be performed by theBS, or network nodes other than the BS. The term ‘BS’ may be replacedwith the term ‘fixed station’, ‘Node B’, ‘evolved Node B (eNode B oreNB)’, ‘Access Point (AP)’, etc.

The embodiments of the present invention may be achieved by variousmeans, for example, hardware, firmware, software, or a combinationthereof. In a hardware configuration, the methods according to exemplaryembodiments of the present invention may be achieved by one or moreApplication Specific Integrated Circuits (ASICs), Digital SignalProcessors (DSPs), Digital Signal Processing Devices (DSPDs),Programmable Logic Devices (PLDs), Field Programmable Gate Arrays(FPGAs), processors, controllers, microcontrollers, microprocessors,etc.

In a firmware or software configuration, an embodiment of the presentinvention may be implemented in the form of a module, a procedure, afunction, etc. Software code may be stored in a memory unit and executedby a processor. The memory unit is located at the interior or exteriorof the processor and may transmit and receive data to and from theprocessor via various known means.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent disclosure. The above embodiments are therefore to be construedin all aspects as illustrative and not restrictive. The scope of thedisclosure should be determined by the appended claims and their legalequivalents, not by the above description, and all changes coming withinthe meaning and equivalency range of the appended claims are intended tobe embraced therein.

1-20. (canceled)
 21. A method for receiving a Synchronization SignalBlock (SSB) by a user equipment (UE) in a wireless communication system,the method comprising: receiving a SSB comprising a primarysynchronization signal (PSS), an secondary synchronization signal (SSS),and a physical broadcasting channel (PBCH); wherein centers ofsubcarriers for the PSS, the SSS and the PBCH are identical, and whereinthe PSS, the SSS and the PBCH are received via a plurality of OrthogonalFrequency Division Multiplexing (OFDM) symbols and a subcarriercorresponding to the centers of subcarriers.
 22. The method of claim 21,wherein the SSS is received via an OFDM symbol located between two OFDMsymbols to which the PBCH is received.
 23. The method of claim 22,wherein the two OFDM symbols are that only the PBCH is mapped.
 24. Themethod of claim 21, wherein the two OFDM symbols comprises DemodulationReference Signals (DMRSs).
 25. The method of claim 24, wherein the DMRSsare mapped at equal interval in each of the two OFDM symbols.
 26. Themethod of claim 21, wherein a number of subcarriers for the PBCSH isgreater than a number of subcarriers for the PSS and the SSS.
 27. Themethod of claim 21, wherein a subcarrier spacing for the SSS isidentical to a subcarrier spacing for the PBCH.
 28. An apparatus forreceiving a Synchronization Signal Block (SSB) in a wirelesscommunication system, the apparatus comprising: at least one processor;and at least one computer memory operably connectable to the at leastone processor and storing instructions that, when executed by the atleast one processor, perform operations comprising: receiving a SSBcomprising a primary synchronization signal (PSS), an secondarysynchronization signal (SSS), and a physical broadcasting channel(PBCH); wherein centers of subcarriers for the PSS, the SSS and the PBCHare identical, and wherein the PSS, the SSS and the PBCH are receivedvia a plurality of Orthogonal Frequency Division Multiplexing (OFDM)symbols and a subcarrier corresponding to the centers of subcarriers.29. The apparatus of claim 28, wherein the SSS is received via an OFDMsymbol located between two OFDM symbols to which the PBCH is received.30. The apparatus of claim 29, wherein the two OFDM symbols are thatonly the PBCH is mapped.
 31. The apparatus of claim 28, wherein the twoOFDM symbols comprises Demodulation Reference Signals (DMRSs).
 32. Theapparatus of claim 31, wherein the DMRSs are mapped at equal interval ineach of the two OFDM symbols.
 33. The apparatus of claim 28, wherein anumber of subcarriers for the PBCSH is greater than a number ofsubcarriers for the PSS and the SSS.
 34. The apparatus of claim 28,wherein a subcarrier spacing for the SSS is identical to a subcarrierspacing for the PBCH.
 35. A user equipment (UE) for receiving aSynchronization Signal Block (SSB) in a wireless communication system,the UE comprising: at least one transceiver; at least one processor; andat least one computer memory operably connectable to the at least oneprocessor and storing instructions that, when executed by the at leastone processor, perform operations comprising: receiving, via the atleast one transceiver, a SSB comprising a primary synchronization signal(PSS), an secondary synchronization signal (SSS), and a physicalbroadcasting channel (PBCH); wherein centers of subcarriers for the PSS,the SSS and the PBCH are identical, and wherein the PSS, the SSS and thePBCH are received via a plurality of Orthogonal Frequency DivisionMultiplexing (OFDM) symbols and a subcarrier corresponding to thecenters of subcarriers.